To connect multiple electrode layers of a three-dimensional memory device to a control circuit, a staircase-shaped contact structure of the multiple electrode layers has been proposed. Further, for the three-dimensional memory device, a method also has been proposed in which a stacked body including multiple sacrificial layers is formed, and an air gap is formed subsequently by removing the sacrificial layers. The stacked body that includes the air gap is supported by a columnar portion that is formed in the stacked body prior to removing the sacrificial layers.